IEEE Power & Energy Magazine - March/April 2020 - 47

estimate the power cable's core temperature and compute
the ampacity of the link.
The idea is worth examining, but the implementation is
actually not that straightforward. If the external optical-fiber
cable is perfectly located for maintenance applications-
detection of changes of surrounding conditions, unknown
heat-source crossings, drying out soils, and so on-it would be
too far from the power cables to accurately capture dynamic
temperature changes. Therefore, this configuration is not
sufficient to implement an effective real-time thermal rating
(RTTR) function.
The challenge is to install sensors as close as possible to
the conductor by integrating optical fibers directly inside
power cables. This should provide quicker and more precise temperature measurements, which will form the basis
of an efficient RTTR solution. To confirm the concept, three
power cables in a new underground link will be equipped
with embedded optical fibers (Figure 3). This pilot project
will determine whether embedded fibers make it possible
to obtain sufficient temperature-variation measurements and,
thus, an effective RTTR system. As a means of comparing
temperature variations, the external optical-fiber cable will
also be monitored.

✔✔ a DTS measuring the temperature along external and

embedded optical fibers and enabling the RTTR
✔✔ a distributed acoustic sensor (DAS) that monitors the
sound near the optical fiber
✔✔ several partial-discharge (PD) sensors to detect small
dielectric breakdowns inside high-voltage (HV)
components
✔ ✔ numerous Rogowski coils for sheath-current measurement.
By monitoring the root causes of major failures, the
implementation of condition-based and predictive-maintenance practices seems possible. This new demonstration
project is designed to maximize the underground-link availability and take full advantage of the link's current rating for
a smarter asset-management strategy.

Experiment for Global
Asset-Management Improvement
Another way to improve grid operation is to reduce the asset
downtime that results from failures (with a duration of days
to weeks) and periodic maintenance actions that require deenergization (lasting hours to days). To that end, various monitoring devices have been installed on a circuit to assess the
equipment-aging process, estimate the state of equipment in
real time, improve maintenance practices, avoid major failures, and optimize repair work when failures do occur. These
monitoring solutions are anticipated to prevent most of the
main causes of failure (Table 1). In total, more than 20 devices
have been deployed:

figure 3. The cable cross-section representation displaying
two optical modules (in red) that have eight optical fibers
each. (Source: Prysmian Group; used with permission.)

table 1. The value of each monitoring device.
Failure Root Cause

Example

Material
defects during
manufacturing or
mounting

Small imperfections in insulation
producing partial discharges and
premature aging
Jacket damage during pulling that
creates a second grounding point

Third-party damage
Surrounding
changes

Grounding failures

march/april 2020	

Monitoring
Solution

Principle

Benefits

PD sensors

Detection and localization
of electrical activity

Rogowski coils

Detection of circulating
induced current

Identification
of defects from
the start, during
warranty period

Undeclared civil works

DAS

Detection, identification,
and localization of hazards

Safety and integrity
of the link

Unknown heat-source crossing

DTS

Ampacity-reliability
assurance

Soil dry-out

RTTR

Detection and localization
of the cause for removal
Detection of ampacity
deviation

Sheath-voltage limiter failure

Rogowski coils

Detection of circulating
induced current

Cable-protectionreliability assurance

ieee power & energy magazine 	

47



IEEE Power & Energy Magazine - March/April 2020

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IEEE Power & Energy Magazine - March/April 2020 - Contents
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IEEE Power & Energy Magazine - March/April 2020 - Cover3
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